Automatic pilot for aircraft



Sept. 23, 1952 w. M. HARCUM ET AL 2,611,560

' AUTOMATIC PILOT FOR AIRCRAFT Filed July 8, 1944 2 SHEETSSHEET 1 W- M. HARCUM ET AL AUTOMATIC PILOT FOR AIRCRAFT Sept. 23, 1952 2 SHEETSSHEET 2 Filed July 8, 1944 |NVENTOR3 W, Ma MAEcu/w Patented Sept. 23, 1952 UNITED STATES AuroMAme :on AI'RQBAFJI' '-'Wi1liam M. Harcum, Garden .City, and Burma Bu t a, '"N- assignors to .1131: Sneflfi' I :Corporatiomfi corp ration nfrDal wa s nlll icatio l lyf t ;1Se ialN ."5 3992 This invention 'relatesito tautomatic pilots for aircraft and, more jparticularly, "to "means for turning and banking the'craft-at thep loper. angle through the automatic pilot. lOurinvention has especial application to the typeof automatic P lot in which both a directionalggyroscope,"or ;other direction maintaining meansand arate-of-turn gyroscope are normally used to controlrtherudder forsteering in azimuth,:but .manyieaturesthereof, are applicable.to'otherltypeszoj pilots.

We are aware that'it has :been proposed to-secure the proper banking .angle for .a predetermined rate of turnbysetting up a:selecte,dra-te of turn through a variable speed drive at the directional gyroscope-V and simultaneously setting a bankin angle proportionalto'therate set up, but such mechanism involvesa variable speeddevice operating in conjunction with the directional gyroscope and other complications which'are eliminated by ourIdevice, andis not a complete solution. 7

According to our invention, we seller entirely the control from theidirectional gyroscope during a turn and dependupon thetnrn being caused primarily by deflection of the. ailerons mhiQhPIimar'ilycause a bank. the resulting turnb ng generally not far from the rate which eliminatessideslip. However, the rate, gyro$cope1is;1eft in control of the rudder, butfitis'ibiasedso-jthatthe signal-therefromdoes not cause'the rudder t oppose the turn; but ratherto. permit-atom 1. the exact rate which isproperifor the'hanis ns angle set in. .The biasing. of the rate gyroscope may be accomplished in. severalways su'chas gby biasing the pick-ofitthereon'from' the turn-bank knob, or by mixing ltheba'sic signhJs'Iromfthe gyrosccpic horizon. and from the .rate gyroscope and applying themodifiedsignal tov the rudder.

In order that the new .CQIlrSB may be continued when the directional gyro.,oontroliis'restored, we have provided means to maintain thQPiCK-Qfi at the directional gyro, when it :isfthrownnnt. at a zero position with. respectfto the gyro so ,that when the gyro. control'is re-established; theplane will continue to fly. on thenew'h eiding which will be showncorrectly on theinourseindicator. Similarly, .we likewise fla l .a .Zeroing control on the pick-offs on .the horizon gyroscope. fliBy this means the .automaticpilot -mayhefth,rown in at any time without endangering. the crait; b cause the pick-offs areealways ma ntained at ,ZBro position and the plane. will. merely. continue, in the assumed attitudeand headin atthe-l imeth ,pilot i thrown in, .until.changed..by.1the,.pi19t turning the controlhandles provided for. the-pur- 58 Claims. (01.244973) -pose. "By-this means theautomatic piletis rendered largelyfoolproof, becauseit doesnqt have to be centralized manually before being thrown Referring to the drawings illustratingfifillfi forms-our invention may assume,

Fig. 1- is a diagrammatic view .of our. improved rudder a-nc't'a'ileron control portions. of anaaliliqmatic -;pi-lot. The elevator controls Jane-0mitt5d i for-- the sake of simp1ic-ity,2 being similar, ingen- -er a'l,-to the-aileron control. 7

li i'gnzshows-a similar view ot a modiiiediorm ;of the invention, --in which a different biasing scheme is employed for the rateeoi-turn-gyroscope, and :i-mwhich a pendulous auxiliary, controller is employed place-of anv airspeed ,correction.

Fig. 1 is intended to show ourinvention .as applied, in-general, to the form of automatic pilot disclosed in the Kenyon and land iEatents 2;2l0;9 16 and 2,238,300dated August 13, 1-940, and -ifl pri ll'5,'-;19 41, respectively. The directional gyroscope is indicated in general at I and the lpiclgaofi or controller thereon is --represented .as. .enclosed withina box 2 the pick-off valve- 1 being turned withg the apparent-movements-of the gyroscope in azimuthfrom-annular-gean 3 secured tofthe .ver-

tical ring 4 of the gyroscope, whichgear meshes with a largeannulargear 5 .turning. sha.-f-t:;.6, on whioh-thepick-off valve I ie-located. E'ourse changes withoutautomatic banking-may. -;be,.ef-

footed-from knob-8- which isshown- .as turning. a

ported sleeve valve 24 surrounding valve through'gears Mand -l0. Anazimuth indicator or porn-passpointer 9 is shownon anextension oi shaft-6. {The pick-olfis-preferab1y ofthe-differential air-flow type show-n in the aforesaid patents, andthe signals therefrom normally .pass through l iipes- +0- and |-0',-*th-r-ough the valve 1H,

and into valve 1 2 ,;wher e they are-mixedwith the gyroscope 15 through linkage t6. '"Bhecombined signals operate the servomotor fl through the usua'ltype of relay valve-I 8 fiirnilarly the ailerons-are normally controlled zpn gyroscope-2jl through gearing 2- l. @oeffect "banking and consequent; turnin g;-we-ha.ve shown .a lgnobf flfwhich', when-turnedg-revolvesthrough ears-1:13.131... he parte s ee s o di 21 which controls the servomotor 28 operating the ailerons.

A second valve 30 is also shown on the shaft 3!, of knob 22 which valve operates primarily to prevent the signals from the rate gyroscope from counteracting the turn through the rudder. For a bankedturn, the knob 22 is not only turned but pushed in, to thereby close a switch within box 32. Closing this switch excites a solenoid 34 which moves the piston valve 35 from the position shown in the drawings, in which the rudder is under the normal control of the combined signals from the directional gyro and rate gyro, to a position in which the signal-from the directional gyroscope is cut out and the rudder placed under the control of the opposing signals of the rate gyroscope and the signal from the valve 36 which is proportional to the bank angle. By this arrangement, the rate gyroscope limits the rate of turn of the craft to correspond to the banking angle set in, so that aproperly -banked turn without side slipping occurs for a predetermined air speed.

Since the proper banking angle varies with air speed as well as rate of turn, we may additionally providemeans for introducing an air speed correction, which may be in the form of a knob 35 settable automatically or by hand in accordance with air speed. Rotation of knob 36 turnsthreaded shaft 3'! and screws threaded sleeve 38 in and out to vary the tension on the centralizing spring 39 for the rate gyroscope, the spring strength being increased with increasing air speed to lessen the rudder throw and therefore the rate of turn (w) for higher air speeds, since centrifugal force (F) varies directly with speed (V) and rate of turn (w) i. e., F Vw. V

In order that the craft may continue upon its new course after a turn, we provide a means to keep the pick-off ports on sleeve 24 at th directional gyroscope continuously centralized or aligned with the butterfly valve 1 on'the directional gyroscope when the control 'from said gyroscope is disconnected, in which position there is zero signal. For this purpose we have shown a transfer valve H, which is normally kept in the upper position under the influence of the compresslon spring 40. When, however, the craft is turned, the valve is pushed downwardly, manually or automatically, disconnecting the pipes Iii,

10' from pipes 42, 12' extending to mixing valve I2 and connecting the former to the opposite ends of chamber 43 containing a flexible diaphragm 4 3. We have shown said valve as automatically operated by solenoid M which is connected with the switch 32 at handle 22, so that whenever the directional gyroscope control is thrown out, the motor 46 is placed in control of the pick-off ports in sleeve 24 to maintain them in alignment or zeroed with respect to the valve I. Therefore a signal from the directional gyroscope in one direction causes the diaphragm to close one pair of contacts to run the motor 56 in one direction, while a reverse signal will cause closure of contacts 47 to run the motor in the opposite direction. The motor 46 is shown as'geared through reduction gearing 48 to a large gear which, as stated, rotates the follow-up sleeve 24 around the directional gyroscope valve so that the ports in the sleeve are maintained aligned with the knife edges on the'valve.

The sleeve 24 of the pick-off valve 1' of the horizon gyro is likewise maintained aligned whenever this control is severed. -The Vail/e26, I

which is similar in function'to valve H, is nor- 4 mally up, as shown, when the pilot is in complete operation. In case, however, the pilot is thrown out, the valve is depressed either manually or automatically to disconnect the ailerons from the gyro control and connect the signals from the gyroscope to a chamber 43', similar to chamber 43 and controlling similar reversing contacts 65 and t? to operate follow-up motor t8. This motor is shown as connected through reduction gearing 48 to the gear 23 connected.

to the sleeve 24, so that the ports in the sleeve are kept centered or aligned at all times with the knife edges on the valve 1.

A master switch 88 is shown for throwing the. pilot, as a whole, in and out. This switch has preferably three positions: (1) the off position, in which the electrical system is paralyzed and the hydraulic system bypassed; (2) the position in which the hydraulic system remains bypassed but the electrical and pneumatic systems are energized so that all pick-oifs are aligned and their output zeroed; and (3) theoperating position in which bypass valve 8! is closed to energize the hydraulic system and the automatic alignment thrown out. In the second position, it will be noted, the solenoids 34, ll and Si are all energizedand the centralizing or aligning motors 45 and 45' ready to operateupon the closing of their reversing switches 45 andjAS'. In the third position, the solenoids .34 and'M and motor 45 are made ready to be placed in circuit with the main supply, the solenoids being energized in case the series switch 32 is cIosed and. the motor being energized when both the switch 32 is closed and one of the pairs of contacts 45' or ill is closed. Position (3) can only be reached by passin through position (2), and hence the automatic pilot can never be thrown in without first aligning the gyro pick-offs, the master switch being so arranged that, by any known delayed action device, sufficient time is allowed for all pick-oifs to be aligned before. position 3 is reached. It

will be understood, of course, that the various dead-endpip'eson which arrows are shown are connected to asource'of air or oil pressure (or vacuum) for energizing the pneumatic and hydraulic systems. V

In Fig. 2 the-showing is similar, except that a different form of biasing or modifying means is employed for the rate gyroscope signal and a diiferent type of corrector. In this form of the invention, the turning of the knob 22 turns directly, through gearing 60, the rotatable ported sleeve 8i of the pick-oif valve 14 controlled from the turn gyroscope I5, so that the zero signal position is changed, thereby eliminating the signal which would otherwise be produced by the gyro scope whenthe aircraft is turning at the rate indicated by the position of the handle 22'. In this form of the invention, no pneumatic signal from the attitude gyroscope enters valve l2.

A further modification is also shown in Fig. 2 which renders unnecessary '"the air speed adjustment of Fig. 1. In this case an additional ruddercontrol is provided'from' a'damped spring signal from the rate gyroscope. Since the signal will be presentfrom the pendulum whenever the craft is banked improperly, this furnishes a ready means fer-adjusting the rudder to maintain the craftturning at the proper angle for the banking angle set in.

Preferably we provide means for obtaining a rate as well as displacement signal from the pendulum. A simple method of securing an approximation of such a combined signal is teemploy an antieipator bellows as a follow-back from the signal to the pendulum, operating somewhat-' onthe principle of the anticipator bellows 3! disclosed-and claimed in the aforesaid Kenyon and Zand Patent No. 2,210,916. :In thisapplication, the-anticipator bellows is shown in the form of a container 10- en'closing a-smaller flexible bellows 1 l and connected through athrottlevalve I3- to a pick-off port T4 by being eom nected-tothe pipe 1-6, which transmits the signal to mixing valve I 2. The interior of the be llows H is connected through a pipe 12 and throttle valve 11 with a pick-off port 14', which also is connected to a pipe 16' also leading the signal to the mixing valve [2. Small bleeds (not shown) are connected to chambers within both container 79 and bellows H, and the movable wall of the bellows H is connected to a spring 18 connected to the pendulum 65 and normally balanced by spring 18'. Alternatively, the bellows may be connected to rotate the housing of the valve 66, as shown in the aforesaid patent. By either arrangement, signals of greater magnitude are obtained for quick movements of the pendulum than for slow movements of equal magnitude, and hence the signals transmitted through pipes 16, T6 are effected both by amount and rate of change of displacement.

In operating an airplane equipped with our improved automatic pilot, the automatic pilot is thrown in by first passing through position (2) of the main switch 80, so that all of the pick-offs are aligned, thus insuring that the craft will continue in the course and attitude prevailing at the time. Properly banked turns are effected through knob 22 or 22', which, when pushed in and turned, banks the craft thereby causing a turn, severs the control from the directional gyroscope, and biases the control from the rate-ofturn gyroscope. The result is that the resulting rate-of-turn is approximately correct for the banking angle set in. During the turn, the pickofi from the directional gyro is kept aligned automatically by motor 46, so that the craft will continue on its new course when the turn is completed.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Means for securing correctly banked turns in an automatic pilot for aircraft including attitude maintaining means for controlling the bank, and direction maintaining means and a rate-ofturn gyroscope for controlling the course, comprising a controller for biasing the bank signals from the attitude maintaining means to cause a bank followed by a turn, a pendulum, and means also operated from said controller for severing the control of course from said direction maintaining means and placing the same under the control of said pendulum and rate-of-turn gyroscope.

Y 2i Means for securing 'c'crreetly -banked turns in an aircraft having-am automatic J pilot includ ing attitude maintaining at he forcontrolling the ailerons, and direction fa'iiitaining means and a rate-of turn' gyroscope fcr ccritrolling the r uddencqmpr'i ing ccntr'ne'r' for biasing the bankfsignals from the attitude maintaining means to cause' 'a bankfollowed by' atur'n, a pen dulum controller-,- and: means operated by said first named controllerfor severing the connection from said direction maintaming means and placing the rudder underth'e-Jointcontrol' of. the pendulum controllerand the-rate gyroscope.

3.-An automatic-banking control device forautomatic pilots for-aircraft'including directional and rate-of-turn gyroscopes and-a rudder servomotor rcr" controlling the er-aft about its yaw axis, a horizon gyroscope and an aileron servomotor for cpntrolling the craft about its bank axis, said respeetiv' gyroscopes having two-part control elements'eneach for said servomotors, and turn control means operable both to shift the relative positions of the parts of the elements of the horizon and rate-of-turn gyroscopes from their normal position and to render the control by the directional gyroscope ineffective.

4. A device as claimed in claim 3, including means for automatically restoring the parts of the control element of the directional gyroscope to a normally aligned position, before the directional gyroscope control is again rendered effective.

5. An automatic banking control device for aircraft automatic pilots including course controlling directional and rate-of-turn gyroscopes, a bank controlling horizon gyroscope, control elements for each of said gyroscopes, and means for causing a correctly banked turn including a single settable means for biasing the bank control elements on the horizon gyroscope and the course horizontal axes, manually settable means for modifying the signal from said generating means to change the crafts attitude, whereby a preset attitude is maintained and saidsignal is zeroed by response of the craft thereto, a second normally inoperative servomotor for zeroing said signal whether modified or not when the pilot is out, a. three position switch for connecting and disconnecting said automatic pilot, said switch in its intermediate position connecting said second servomotor to said signal to zero the same, whereby the attitude of the craft is never suddenly changed when the pilot is thrown in.

'7. Means for securing correctly banked turns in an aircraft having an automatic pilot including attitude and directional gyroscopic means, each having a pick-off means whose output normally controls the ailerons and rudder, respectively, and a spring centralized rate-of-turn gyroscope also normally controlling the rudder, comprising a manually operated controller for biasing the bank signals from the pick-off on the attitude maintaining means to cause a bank followed by a turn, means also operated from said controller for severing the directional pick-off from control of the rudder, means also operated by said controller for biasing the control signal from the rate gyroscope by an amount proportional to the angle of bank set in, and motive means brought into action during turns and actuated from the output of said directional pick-off for maintaining it at zero during turns so that on completion of the turn the craft will continue to fly on the new heading.

8. Means for securing correctly banked turns in an aircraft having an automatic pilot, as claimed in claim 7, which also has a means for proportionally increasing the stifiness of the centralizing springs of the rate gyroscope with increasing air speed to lessen the rudder displacement.

WILLIAM M. HARCUM. GIFFORD BULL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Bates Dec. 29, 1936 Wunsch Aug. 16, 1938 Fischel Nov. 22, 1938 Roland Apr. 23, 1940 Zand et al. Apr. 15, 1941 Hanson et al. Jan. 27, 1942 Matthews May 19, 1942 Carlson July 27, 1943 Kronenberger Aug. 22, 1944 Frische Feb. 11, 1947 Hansen Feb. 18, 1947 Noxon et al. July 25, 1950 

